The position and speed of a hydraulic elevator may be managed by an elevator control system that regulates the flow of hydraulic fluid through an integral valve in fluid communication with a movable plunger mechanically coupled to the elevator. A rate at which hydraulic oil flows through a bypass channel in the integral valve controls the motion of the plunger and correspondingly controls acceleration and deceleration of the elevator. The elevator may move up or down its hoistway at a selected service velocity until the elevator approaches a destination landing or an end of the hoistway. As the elevator approaches a destination landing, perhaps after a passenger in the elevator activates an electrical switch for selecting his or her destination, the elevator decelerates from the service velocity and opens the elevator doors, preferably after stopping with the elevator floor level with the landing. After closing the doors, the elevator accelerates to the service velocity on its way up or down the hoistway to a next destination.
After receiving a stop command for a selected landing, the elevator controller begins decelerating a moving elevator after the elevator activates a slowdown actuator. The slowdown actuator is positioned in the hoistway within a fixed distance of the landing. The slowdown actuator may be activated, for example, by a cam on the elevator closing an electrical switch attached to a stationary support structure in the hoistway. The elevator controller may ignore slowdown actuators for landings between the elevator's start position and the selected destination landing. The fixed distance between a slowdown actuator and its associated landing, also referred to herein as a static slowdown distance, may be determined by testing the elevator at a selected combination of elevator load and hydraulic oil temperature. The static slowdown distance may remain fixed during the service lifetime of the elevator and related components. After responding to the activation of a slowdown actuator, the elevator controller decelerates the elevator to a stabilized leveling speed. The integral valve is fully closed when a stationary leveling actuator activated by the elevator indicates that the elevator floor has reached the level of the landing.
An optimal value of static slowdown distance required for an elevator to achieve a level stop with a landing depends in part on the load carried by the elevator and the temperature of the hydraulic oil. The viscosity of hydraulic oil changes with temperature. As hydraulic oil flows through pumps, valves, and other parts of the elevator's hydraulic system, energy transfers into the oil, increasing the oil's temperature and decreasing its viscosity. Changes in viscosity cause related changes in the flow rate of hydraulic oil through the integral valve and cause related changes in the acceleration and deceleration of an elevator. The hydraulic oil in an elevator subjected to frequent use may experience sufficient heating of the hydraulic oil to affect elevator acceleration, ride quality, travel time, and other factors related to elevator operation. A static slowdown distance for each landing may preferably be selected to be large enough to enable an elevator to achieve leveling over the full ranges of loads and hydraulic oil temperatures expected during operation of the elevator. The time duration from initiation of slowdown until completion of leveling for elevators with static slowdown distances has been measured at up to six seconds per stop. If the static slowdown distance is too small for a particular combination of load and hydraulic oil temperature, leveling may not be completed by the time the elevator doors open. If the static slowdown distance larger than an optimal value, leveling may take too long, increasing elevator travel time, increasing wear on pumps, valves, and other hydraulic components, and increasing an amount of electricity consumed to operate the elevator.
Because elevator loads and hydraulic oil temperatures both vary during elevator operation, static slowdown distances affect the rates at which an elevator accelerates and decelerates. Elevators with static slowdown distances may operate with slower travel times, longer slowdown times, greater equipment wear, and greater energy consumption than would be the case if the elevator were operating at the specific values of elevator load and oil temperature used to select the static slowdown distance.
Elevator leveling is an important aspect of passenger comfort and safety. If an elevator stops with a vertical offset between the elevator floor and a landing, a passenger may stumble or fall when entering or exiting the elevator. A passenger may experience motion discomfort or may stumble or fall if an elevator accelerates or decelerates too quickly. However, if leveling takes too long or acceleration and deceleration are too slow, passengers may complain about travel times being too long.